meson: Fix docs generation with PyGObject 3.52

PyGObject 3.52 switched from gobject-introspection’s libgirepository 1.0
to glib’s libgirepository 2.0. As a result, the Python script would
no longer be able to find the `GIRepository` 2.0 typelib:

    (process:1944): GLib-GIRepository-DEBUG: 15:25:14.521: Ignoring GIRepository-2.0.typelib because this libgirepository corresponds to GIRepository-3.0.typelib

We could update the script to support both versions of the typelib
but it is not really necessary. It was only used to add extra directories
from `$LD_LIBRARY_PATH` and the CLI argument to repository’s library path
but libgirepository already supports using `LD_LIBRARY_PATH` directly:
https://docs.gtk.org/girepository/method.Repository.prepend_library_path.html

src/libnm-client-impl/meson.build

@@ -209,7 +209,6 @@ if enable_introspection
         'LD_LIBRARY_PATH=' + ld_library_path,
         python_path,
         gen_gir_cmd,
-        '--lib-path', meson.current_build_dir(),
         '--gir', libnm_gir[0],
         '--output', '@OUTPUT@',
         '--target', name

tools/generate-docs-nm-settings-docs-gir.py

@@ -6,26 +6,9 @@
 from __future__ import print_function, unicode_literals
 import xml.etree.ElementTree as ET
 import argparse
-import os
 import gi
 import re
 
-gi.require_version("GIRepository", "2.0")
-from gi.repository import GIRepository
-
-try:
-    libs = os.environ["LD_LIBRARY_PATH"].split(":")
-    libs.reverse()
-    for lib in libs:
-        GIRepository.Repository.prepend_library_path(lib)
-except AttributeError:
-    # An old GI version, that has no prepend_library_path
-    # It's alright, it probably interprets LD_LIBRARY_PATH
-    # correctly.
-    pass
-except KeyError:
-    pass
-
 gi.require_version("NM", "1.0")
 from gi.repository import NM, GObject
 
@@ -354,13 +337,6 @@ def main(gir_path_str, output_path_str, output_target):
 
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
-    parser.add_argument(
-        "-l",
-        "--lib-path",
-        metavar="PATH",
-        action="append",
-        help="path to scan for shared libraries",
-    )
     parser.add_argument(
         "-g",
         "--gir",
@@ -384,8 +360,4 @@ if __name__ == "__main__":
 
     args = parser.parse_args()
 
-    if args.lib_path:
-        for lib in args.lib_path:
-            GIRepository.Repository.prepend_library_path(lib)
-
     main(args.gir, args.output, args.target)